According to classical optics, transmission of light through a sub-wavelength aperture in a metal film is extremely small when its diameter d is significantly smaller than the wavelength λ, and is predicted to follow the Bethe limit T/f˜(d/λ)4, where T/f denotes the transmission normalized to the area occupied by the aperture. Recently it has been reported in U.S. Pat. Nos. 5,973,316 and 6,236,033 and in Nature, Vol. 391, pp. 667-669, all incorporated herein by reference in the entirety, that extremely high transmission through sub-wavelength aperture(s) in a metal film can be obtained when the incident light is resonant with surface plasmon in the metal film.